The present invention relates to an information apparatus which transmits information to a user by body sensation of vibration. For example, it relates to a vibration motor and an apparatus using this motor, such as a cellular phone, an information terminal and a watch and so on. The motor and the apparatus can be smaller, save space, consume less power and have additional functions.
Particularly, the vibration motor in this invention is formed of a brushless motor without using a position-detector of a rotor, and this vibration motor is suitable for detecting back-electromotive-force (BEMF) and to be driven. This vibration motor is equipped with a motor driver which realizes various controls such as speed-control, short brake, forward rotation, reverse rotation, start and stop and so on.
A conventional sensorless-brushless-motor driver which has no position-detecting device is described as follows. When the motor rests or rotates very slowly, such that back-electromotive-force (BEMF) generated at driving coils of the motor cannot be detected, an ON-OFF state of the driving-coil of each phase is switched sequentially by supplying timing pulses from outside. The motor then starts from its resting state. Such starting-circuit means is disclosed in Japanese Patent Application Non-Examined Publication No. H02-206394. Driving-circuit means, which detects BEMF generated at driving-coil and produces optimum driving timings after the motor starts, is known in Japanese Patent Application Non-Examined Publication No. H03-89889.
It is known using means that BEMF (voltage value) of the motor is proportional to the r.p.m. of a motor as speed-control means of the motor. As a vibration device, means of setting frequency and amplitude of vibration arbitrarily is disclosed in Japanese Patent Application Non-Examined Publication No. H08-149182. Means for changing vibration depending on the time is disclosed in Japanese Patent Application Non-Examined Publication No. H09-130840.
FIG. 12 is a driving circuit diagram of a vibration motor (sensorless-brushless-motor) in accordance with a first prior art example.
As shown in FIG. 12, each terminal of stator coils 802, 803 and 804 is connected with power-input terminal 303. BEMF generated from each coil 802, 803 and 804, are converted to rectangular pulses by comparators 721, 722 and 723, which are then input to timing circuit 113. Timing circuit 113 delays leading edges and trailing edges of the rectangular pulses by electrical angle 30 degrees and produces timing signals to start powering.
Phase-switching circuit 114 inputs the timing signals from timing circuit 113 and outputs phase-switching signals to power amplifier 740. Phase-switching circuit 114 supplies base electric currents to transistors 792, 793 and 794 forming output-circuit 115 during 120 degree in electrical angle through power amplifier 740. Electric currents are carried in coils 802, 803 and 804 sequentially at the timings produced by timing circuit 113 during 120 degree in electrical angle respectively.
Power amplifier 740 is formed such that it can control the base electric current of transistors 792, 793 and 794 based on an output signal of error amplifier 780. Feedback is controlled such that the motor can rotate at the r.p.m. where reference voltage 781 and synthesized voltage are balanced, whereby synthesized voltage is synthesized between an output voltage of FV(frequency/voltage)-converting circuit 770 and an applied voltage of control-input terminal 701. FV converting circuit 770 converts amplitude of BEMF generated at coils 802, 803, and 804 to a voltage and outputs the resultant voltage during off-time of transistors 792, 793 and 794. In other words an r.p.m. of the motor is converted to the voltage by FV converting circuit 770, and the voltage feedbacks to error amplifier 780 which controls motor operating current, so that a closed loop circuit is formed. The r.p.m. of the motor is then controllable by an applied to voltage to controlling-input terminal 701.
Capacitor 901 is used for a starting-oscillator. Capacitor 902 is used for producing ON-OFF-timing. Capacitor 903 is used for compensating phase of closed loop. Oscillating-circuit 710, power supply 750, switch 751 and resistor 761 are used for starting motor. The description of these elements are omitted here.
FIG. 13 is a circuit diagram of a vibration device in accordance with a second conventional example. FIG. 14 is a circuit diagram of a vibration device in accordance with a third conventional example.
As shown in FIG. 13, motor 1 of the second conventional example is equipped with vibration-generating means (not shown) formed of unbalanced load at a rotor, and generates vibration by rotating the motor. Battery 2 is a secondary battery, e.g. a lithium ion battery. Transistor 11 is coupled between battery 2 and motor 1, and transistor 12 and resistor 21 are coupled in series between them. Selecting terminal 31 or 32 is brought into contact with the minus side of the battery, thereby selecting a magnitude of vibration.
In the third conventional example shown in FIG. 14, a section, which corresponds to resistor 21 of the second conventional example of FIG. 13, is replaced with variable resistor 24. A resistor value to be inserted to motor 1 in series is arbitrarily changeable by changing a value of variable resistor 24 with a signal of controlling-input terminal 33, whereby a vibration magnitude and a vibration period are changeable
FIG. 15 is a speed-controlling circuit diagram of a vibration device in accordance with a fourth conventional example and disclosed in Japanese Patent Application Non-Examined Publication No. S55-109185. FIG. 16 is a speed-error-detecting circuit diagram of the vibration device.
As shown in FIG. 15, first regular pulse-width-producing circuit 405 comprises N-ary counter, which uses a trailing edge of output signal of pulse-forming circuit 403 as a trigger signal.
The N-ary counter holds level xe2x80x9c1xe2x80x9d while the counter counts a number of output pulse of reference oscillator 108, namely a reference clock, up to N pulses, and holds level xe2x80x9c0xe2x80x9d after counting N pulses. Second regular pulse-width-producing circuit 406 comprises M-ary counter, which uses a trailing edge of an output signal of first regular pulse-width-producing circuit 405 as a trigger signal. The M-ary counter holds level xe2x80x9c1xe2x80x9d while the counter counts a number of reference clock up to M pulses, and holds level xe2x80x9c0xe2x80x9d after counting M pulses. Pulse-synthesizing circuit 407 synthesizes output pulses of regular pulse-width-producing circuits 405 and 406, and converts it to a pulse width corresponding to a speed error of motor 401. In other words, speed-error-detecting circuit 411 comprises pulse-width-producing circuits 405, 406 and pulse-synthesizing circuit 407.
Filter circuit 408 smoothes an output pulse of pulse-synthesizing circuit 407 and converts it to a direct current voltage. Low-frequency-compensating circuit 409 amplifies low frequency component of outputs from filter circuit 408. Motor-driving circuit 410 amplifies output power of low-frequency compensating circuit 409.
FIG. 16 is a diagram of speed-error-detecting circuit 411 in FIG. 15. As shown in FIG. 16, N-ary counter 421 has reference-clock-input terminal CK, output terminal DOB and clear terminal CL. Differentiating circuit 422 differentiates a trailing of a signal entering point B, and outputs a trigger signal. Set-Reset flip-flop (SR flip-flop) circuit 423 resets and sets responsive to the trigger signal at level xe2x80x9c0xe2x80x9d. First regular pulse-width-producing circuit 405 is composed of counter 421, differentiation circuit 422 and RS flip flop 423. Contents of the second regular pulse-width-producing circuit 406 are the same as first regular pulse-producing circuit 405 except count numbers N and M.
Resistors 426 and 427 supply a current to each base of PNP transistor 430 and NPN transistor 431. Resistors 428 and 429 prevent leak electric currents of transistors 430 and 431. Pulse synthesizing circuit 407 comprises OR circuit 424, AND circuit 425, resistors 426, 427, 428, 429 and transistors 430, 431.
A voltage level of collector-common-connecting-point G of both the transistors mentioned above can be hold at the following three states. When an r.p.m. of the motor is faster than a reference speed, an output cycle of frequency generator 402 in FIG. 15 is shorter than a reference cycle made by adding a number of pulses counted by N-ary counter and that of by M-ary counter. In this case, point G, which is an output point of pulse synthesizing circuit 407, operates in electric-current-absorbing mode and absorbs an electric current from filter circuit 408, thereby reducing an output voltage of filter circuit 408. As a result, the r.p.m. of motor 401 decreases through low frequency compensating circuit 409 and motor-driving circuit 410, and the output cycle of frequency-generator 402 becomes longer.
On the contrary, when the r.p.m. of the motor is slower than the reference speed, point G operates in electric-current-bursting mode and raises an output voltage of filter circuit 408. As a result, the r.p.m. of motor 401 increases through low frequency compensating circuit 409 and motor-driving circuit 410, and the output cycle of frequency-generator 402 becomes shorter.
When motor 401 rotates (at the reference speed) constantly, transistors 430 and 431 continue off-states and become high impedance states, so that an input and an output of electric current at point G is disappears and the output voltage of filter circuit 408 keeps a constant level. As a result, the r.p.m. of motor 401 keeps constant.
However, when the conventional sensorless-brushless-motor driver is formed of a one chip semiconductor device (IC), starting-circuit capacitor 901, ON-OFF-timing-producing capacitor 902 and closed-loop-phase-compensating capacitor 903 are difficult to be put inside the IC. Because these capacitors are required to have at least 1 nF, the sizes of the capacitors may become big. The capacitors are thus exterior to the IC.
A starting-circuit of the conventional sensorless-brushless-motor driver produces reference clock with a CR oscillator comprising a capacitor and a resistor. The reference clock should be a low frequency (approx. several tens Hzxe2x80x94several hundreds Hz).
In such a case, a capacity of the capacitor should be increased, therefore it is difficult for the IC to integrate the capacitor, and a capacitor having a large capacity is typically required to be a component exterior to the IC. A charge and a discharge current are desirably small in order to produce a low frequency reference clock when a capacity of the capacitor is small, whereby accuracy of oscillation degrades due to the influence by a fine leak electric current.
Motor-speed-control means of the first conventional example in FIG. 12 uses the fact that a voltage level of BEMF of the motor is proportional to an r.p.m. of a motor. Even if a reference voltage corresponding to a reference r.p.m. of a motor is designed precisely in the IC, BEMF of the motor depends on characteristics of the motor. The reference voltage suited to the characteristics of the motor is required because the r.p.m. changes in accordance with a change of the characteristics of the motor.
In a small vibration motor driving system recently used in a small and a light weight apparatus, when the number of exterior components are reduced for downsizing and weight reduction, a dispersion of the r.p.m. of the motor occurs in manufacturing motors, because the r.p.m. is determined by the characteristics of the motor as discussed above.
One of conventional apparatuses aims at better performance for users to select vibration perceivable easily or the appratus increases magnitude of vibration gradually. Conventional r.p.m. control means based on the voltage of BEMF changes the r.p.m. by changing a direct current voltage level after supplying the direct current voltage level functioning as a speed-instruction from the outside. In such a case, the r.p.m. depends on respective motors, because r.p.m. accuracy disperses depending on the characteristics of the motor.
A vibration motor comprises the following elements:
(a) a rotor having an unbalanced load,
(b) a stator having a plurality of coils having different phases respectively and
(c) a motor driver coupled with the coils and rotating the rotor.
The motor driver including;
(c-1) a starting-circuit for applying starting torque to the motor;
(c-2) a back-electromotive-force(BEMF)-detecting circuit for detecting BEMF of each phase of the motor and outputting BEMF signals corresponding to the BEMF;
(c-3) an output-driving circuit having;
a timing-generating circuit for producing at least one signal to switch An ON-OFF state sequentially for the coils based on the BEMF signals, and
(c-4) a speed-controlling circuit having a reference-cycle-generating circuit for generating a reference cycle signal and a cycle-comparing circuit for comparing a cycle of the reference cycle signal with a cycle of the BEMF detecting signal so that ON-OFF period to power said coils is effected responsive to output from said cycle comparing circuit.